Down-hole pumps have been used for a considerable period of time in the production of liquids from oil wells. Such pumps are generally of two types, electrically driven centrifical pumps located down in the well and reciprocating piston pumps driven by sucker rods from the surface. Both types are inserted in an oil well at the lower end of the production tubing string which carries the produced hydro-carbon liquid to the surface.
Both types of pumps have their drawbacks. The electrically driven pumps requires electrical conduit to carry power down-hole to the pump and special well-heads have been developed to accommodate the electrical connections required. See for example U.S. Pat. No. 3,473,149 issued to Cugini, et al.
The reciprocating piston-type pumps requires connection through the well-head to a reciprocating mechanism on the surface. The connection is through sucker rods which connect the piston rod of the down-hole pump to the surface unit. Sucker rods are known in the art and may be made of steel or fiberglass. Surface reciprocating units are common as evidenced by the many "grasshoppers" which may be seen in oil fields. The units may be of a variety of types, but one common type is the beam type pump as manufactured by Lufkin Industries or USS Oil Well.
Reciprocating plunger type down-hole pumps are known in the art. Some specific examples are illustrated in U.S. Pat. Nos. 615,470; 1,020,051; 1,156,882; 1,519,585; 1,550,963; 2,281,899; and 2,360,139.
All of the above disclosed pumps have a multiplicity of moving parts and/or sealing surfaces. Some, such as 2,281,899, for example, have specially designed check valves to prevent back-flow of oil on the intake stroke and others, such as 2,360,139, have double acting pistons for pumping fluids on both strokes of the plunger.
Wherever there is a sealing surface, there is a likelihood of a leak. Also, wherever there are moving parts, there is the possibility of wear. The highly corrosive atmosphere and abrasive material in the pump liquid contributes to leakage and wear. Simple pumps with few moving parts can be protected more easily against corrosion and abrasion, thus reducing leakage and wear.
None of the disclosed pumps has a simple single valve which operates in response to flow of liquid to open and close the intake-outlet at ports in one movement.